A Synchronous Optical Network, also known as a SONET, is a networking standard for connecting fiber-optic transmission systems. SONET is the American National Standards Institute standard for synchronous data transmission on optical media. The “synchronous” designation means that portions of the data stream may be cross-connected to other portions without demultiplexing. As such, all component portions of the SONET signal may be tied to a single reference clock.
A SONET is considered to be the foundation for the physical layer of the broadband ISDN (BISDN). The international equivalent of SONET is synchronous digital hierarchy (SDH). Together, they ensure standards so that digital networks can interconnect internationally and that existing conventional transmission systems can take advantage of optical media through tributary attachments.
SONET defines interface standards at the physical layer of the OSI seven-layer model. The standard defines a hierarchy of interface rates that allow data streams at different rates to be multiplexed. SONET establishes Optical Carrier (OC) levels from 51.8 Mbps (about the same as a T-3 line) to 2.48 Gbps.
SONET technology uses architecture called SONET rings. SONET rings are known as self-healing rings. In this manner, SONET rings use two or more transmission paths between network nodes, which are typically optical or digital cross-connects (DCSs) or add/drop multiplexers (ADMs). Consequently, if there is a break in one line, the other may still be available. Typically, the most fault-tolerant architecture is the four-fiber bi-directional ring.
Within the SONET, channels are designated for alarms, maintenance, control, monitoring, administration and communication needs between two section terminating equipments. One such channel is the data communication channel (DCC). The DCC is the upper level bandwidth of the network that allows for communication between parts of the network and is utilized for management, enabling IP addressing and Simple Network Management Protocol (SNMP) access. Typically, the DCC is 3 bytes and is treated as one 192 kbs data channel for the transmission of alarms, maintenance, control, administration as well as other network element communication needs that occur between the SONET nodes. The DCC is also used for testing the functionality of the SONET. In this manner, active test signals are transmitted through the SONET ring, while the ring is simultaneously monitored for any malfunctions.
Currently, a variety of SONET testing device exist. For example, one testing device may be used to transmit an active test signal through the SONET (in what is commonly called insert/drop mode) while simultaneously monitoring (commonly called monitor mode) the ring for faults. Equipment having these two features are, however, quite expensive. Alternatively, two testing devices can be used to simultaneously perform the same insert/drop and monitoring functions. In this manner, one testing device can be used to perform the insert/drop and the other to act in the monitor mode. Despite being less expensive, this configuration requires more manpower to set up and perform the test.
Consequently, there is a need therefore for a low cost SONET testing device that can be used to simultaneously test a SONET using the insert/drop mode and the monitor mode.